Nerve stimulation can be applied in the treatment of a range of conditions. The nerve stimulation may be applied to control muscle activity or to generate sensory signals. Nerves may be stimulated by surgically implanting electrodes in, around or near the nerves and driving the electrodes from an implanted or external source of electricity.
The phrenic nerve normally causes the contractions of the diaphragm that are necessary for breathing. Various conditions can prevent appropriate signals from being delivered to the phrenic nerve. These include:                chronic or acute injury to the spinal cord or brain stem;        Amyotrophic Lateral Sclerosis (ALS);        disease affecting the spinal cord or brain stem; and,        decreased day or night ventilatory drive (e.g. central sleep apnea, Ondine's curse).These conditions affect significant numbers of people.        
Mechanical ventilation may be used to help patients breathe. Some patients require chronic mechanical ventilation. Mechanical ventilation can be lifesaving but has a range of significant problems. Mechanical ventilation:                tends to provide insufficient venting of the lungs. This can lead to accumulation of fluid in the lungs and susceptibility to infection.        requires apparatus that is not readily portable. A patient on ventilation is tied to a ventilator. This can lead to atrophy of muscles (including breathing muscles) and an overall decline in well being.        can adversely affect venous return because the lungs are pressurized.        interferes with eating and speaking.        requires costly maintenance and disposables.        
Phrenic nerve pacing uses electrodes implanted in the chest to directly stimulate the phrenic nerve. The Mark IV Breathing Pacemaker System available from Avery Biomedical Devices, Inc. of Commack, N.Y. USA is a diaphragmatic or phrenic nerve stimulator that consists of surgically implanted receivers and electrodes mated to an external transmitter by antennas worn over the implanted receivers. Implanting electrodes and other implantable components for phrenic nerve pacing requires significant surgery. The surgery is complicated by the fact that the phrenic nerve is small (approx. diameter 2 mm) and delicate. The surgery involves significant cost.
Laproscopic diaphragm pacing being developed by Case Western Reserve University bio-medical engineers and physician researchers is another technique for controlling breathing. Devices for use in Laproscopic diaphragm pacing are being developed by Synapse Biomedical, Inc. Laproscopic diaphragm pacing involves placing electrodes at motor points of the diaphragm. A laparoscope and a specially designed mapping procedure are used to locate the motor points.